Extrusion press for hydrostatic extrusion with a billet-holding piston in the pressure chamber

ABSTRACT

A press for the hydrostatic extrusion of tubes includes a billet holder through which passes a mandrel. There is an annular rib on the front face of the billet holder which is engageable with the back end of the billet. There are also passages opening from the rear of the billet holder into the spaces within and outside of the annular rib. Resiliently held valves with different spring pressures acting thereon control these passages. A billet is inserted having an opening in its front end smaller than the diameter of the mandrel, and upon the application of pressure to a mandrel holder the mandrel is driven through the front end of the billet, enlarging the opening therein, while the pressure in the spaces referred to above prevents harmful tensile stresses in the die.

United States Patent Syvakari 1 July 8, 1975 [54] EXTRUSION PRESS FOR HYDROSTATIC 3,751,957 8/1973 Nilsson 72/60 3,751,958 8/1973 Nilsson et a1. 72/60 EXTRUSION WITH A BILLET-HOLDING PISTON IN THE PRESSURE CHAMBER [75] Inventor: Pertti Syvakari, Helsingborg,

Sweden [73] Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden [22] Filed: Sept. 30, 1974 [21] Applv No.: 511,301

[30] Foreign Application Priority Data Oct. 12, 1973 Sweden 73138745 [52] US. Cl 72/60; 72/264 [51] Int. Cl. B21C 23/08 [58] Field of Search 72/60, 264, 268, 269, 272

[56] References Cited UNITED STATES PATENTS 3,531,965 10/1970 Nilsson 72/60 3,702,555 11/1972 Larker et al 72/60 Primary Examiner-Richard .l. Herbst [57] ABSTRACT A press for the hydrostatic extrusion of tubes includes a billet holder through which passes a mandrel. There is an annular rib on the front face of the billet holder which is engageable with the back end of the billet. There are also passages opening from the rear of the billet holder into the spaces within and outside of the annular rib. Resiliently held valves with different spring pressures acting thereon control these passages. A billet is inserted having an opening in its front end smaller than the diameter of the mandrel, and upon the application of pressure to a mandrel holder the mandrel is driven through the front end of the billet, enlarging the opening therein, while the pressure in the spaces referred to above prevents harmful tensile stresses in the die.

3 Claims, 4 Drawing Figures wa wmm R I975 mmmmwm 0 T Fmw mm QR A m i/ m M a Q R 5% aw i ,9, "mm N t 1 EXTRUSION PRESS FOR HYDROSTATIC EXTRUSION WITH A BILLET-HOLDING PISTON IN THE PRESSURE CHAMBER BACKGROUND OF THE INVENTION I. Field of the Invention The invention relates to hydrostatic extrusion.

2. The Prior Art The present invention relates to a press for hydrostatic extrusion of the type having a billet holder shaped as a piston which divides the pressure chamber into two spaces and, which, when pressure medium is supplied to one of these spaces, achieves a difference in pressure between the two spaces when the axial movement of the piston is slowed down. When a billet is inserted, the billet and a die are placed straight in front of the opening of a movable high-pressure cylinder forming part of the pressure chamber, after which the pressure chamber is moved in over the end of the billet, a pressure medium then being supplied to the space on one side of the piston. The piston is then displaced towards the billet. When its movement ceases, a pressure difference arises between the two sides of the piston and an axial holding force occurs because of the pressure difference which keeps the billet and the die pressed against a die support. The inserting member can now be removed and the cylinder be further moved in over the billet and the die so that the pressure charn her is completely closed and the extrusion can be performed. Presses of said types are described more fully in US. Pat. Nos. 3,531,965 and 3,751,958.

SUMMARY OF THE INVENTION In the extrusion of tubes, a tubular billet is the starting material and a mandrel for shaping the hole in the tube is used. This mandrel is part of a unit in the pressure chamber, which is axially fixed by spacing tubes and sealing rings at the ends of the high-pressure chamber. When the billet is inserted, a perfect seal must be achieved between the billet point and the die as well as between the billet point and the mandrel. A hollow billet may be used which, at the front end, has a diameter which is less than the diameter of the mandrel. The mandrel is pressed into this front path in connection with the insertion of the billet, thus obtaining a seal. The mandrel must then be axially fixed and the forces will be taken up by a spacing tube and a sealing ring. The permissible axial force is limited and in many cases insufficient for pressing in the mandrel. The invention makes it possible to press in the mandrel without subjecting said sealing ring to axial forces from the mandrel by way of said support tube, by making use of the pressure medium in a suitable manner and achieving suitable pressure differences between various spaces in the pressure chamber.

According to the invention the billet holder is provided with elements which are intended to seal against the end of a billet inserted in the pressure chamber, thus separating a first space between the billet and the cylinder wall from a second space between the billet and the mandrel. Extending axially through the billet holder are two separate flow paths. A first flow path opens out into the space between the billet and the cylinder wall and a second flow path opens out into the space between the billet and the mandrel. In the flow paths there are valve members which open the flow paths at different pressure differences between the spaces of the billet holder. The mandrel is axially displaceably arranged and is pressed into the portion of the hollow billet having the smaller diameter by means of the pressure medium.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in more detail with reference to the accompanying drawings.

FIG. I shows a pressure chamber in a press for hydrostatic extrusion according to the invention and FIG. 2 in more detail the billet holder and the die and the pressure chamber parts around these.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the figures, I designates a pressure chamber formed from a high'pressure cylinder 2, a pressuregenerating punch 3 and a die 4 resting on a die support 5. The cylinder 2 may be built up of an inner tube 6 (liner), which is surrounded by an outer prestressed tube 7, possibly a prestressed strip sheath, and end pieces 8 and 9. These end pieces act as support for high-pressure seats 10 and I1. Between these seals there are two spacing tubes 12 and 13, a holder I4 for a mandrel l5 and a spacing tube 16 which transmits axial forces, acting on the mandrel during the extrusion, to the die 4. The mandrel I5 is provided with a head 17 which is able to move in the bore hole I8 between the seat I9 in the holder 14 and the lid 20. At the bottom of the figures the mandrel is shown in its left limit position before it has been pushed into the front part of the billet. At the top of the figures the mandrel is shown in its right limit position completely inserted into the billet. During extrusion it is located in this position. In the mandrel holder 14 is a channel 2].

The billet holder 25 divides the pressure chamber into two spaces 26a, 26b and 27a, 27b. The space between the pressure-generating punch 3 and the billet holder 25 is divided into two parts 26a and 26b by the mandrel holder 14: The other space is divided into two parts, one part 27a between the billet 28 and the spacing tube 16, and another part 27b between the billet 28 and the mandrel F5. The spaces 27a and 27b are separated from each other by the annnular rib 30 on the billet holder 25. Through the billet holder there are two separate flow paths. A first flow path is formed by the channel 31, the valve chamber 32 and the channel 33. This opens out into the space 27a. A second flow path is formed by the channel 34, the valve chamber 35 and the channel 36. opens out into the space 27b. In the valve chambers there are valve members 37 and 38, respectively, which are influenced by springs 39 and 40 with different strengths. In the billet holder is a bore hole 41 with a bushing, fitting on the mandrel [5, which is secured by a locking ring 43. When the dimension of the tube is to be changed, the mandrel 15 and said bushing 42 are changed. In the end piece 9 is a seal 45 sealing between the opening in the end piece and the pressure-generating punch 3, and a channel 46 through which the space 26a can be supplied with pressure medium when the pressure-generating punch has the position shown in the figure.

As is clear from FIG. 2, the seal 10 and the seal II, which is not shown here, are of the types having an outer sealing ring 50 and an inner sealing ring 5]. The ring 50 in the seal 11 transmits axial forces on the mandrel l5 acting to the left if the mandrel is completely axially fixed so that it is forced into the billet when the billet and the die are moved into the pressure chamber. This ring should not be subjected to great forces.

As shown in FIG. 2, the billet holder 25 may consist of a disc 53 having a bore hole 41 for the bushing 42 for the mandrel l and a number of bore holes 54 and 55 for a number of valve units consisting of valve housings 56 and 57, respectively, with valve cones 58 and 59, respectively, which are influenced by springs 60 and 61, respectively, of different strengths. The channels 3 1 and 34, respectively, are then situated in the valve housings and the channels 33 and 36, respectively, are positioned in the disc 53. in the valve housings there are radial openings 63 and 64, respectively.

The mode of operation of the press is as follows. When a billet and a die are inserted, they are placed straight in front of the cylinder, whereupon the cylinder is pushed to the right, a little bit over the billet. At the same time pressure medium is supplied to the spaces 26a and 26b through channel 46 in the end piece 9. The valves in the billet holder 25 achieve a pressure difference between the two sides of the billet holder so that a force is obtained which displaces the holder 25 towards the billet 28 and presses the billet against the die 4 and the die support 5. The billet and the die are retained in this position by the force of the billet holder. The inserting appliance can be removed and the cylinder 2 be moved in over the billet to the position shown in the figures. The hole 66 at the billet point 65 has a smaller diameter than the mandrel 15. When the billet point 65 engages the mandrel 15, it moves the mandrel to-the left, as shown in the lower halves of the figures. By raising the pressurein the space 260, an axial force of such magnitude can be obtained that the mandrel is pressed into the front part 65 of the billet to the position shown in the upper halves of the figures. This pressure required for inserting the mandrel is much higher than the pressure required for holding the billet and the mandrel together. By using valve members 37 and 58, respectively, which open at a relatively low pressure, in the first flow path opening out in the space 270, the space 27d, can be filled with pressure medium before the pressure in the spaces 26a and 26b is raised to the level required for inserting the mandrel 15. This means that the axial force operating on the billet is limited, and also that the die 4 receives a radial supporting pressure. In this way detrimental tensile stresses are eliminated in the die when the pressure is raised to the level required for inserting the mandrel, so that seal between the mandrel and the billet is obtained. When the pressure is further increased, the valve members 38 and 59, respectively, in the other flow path, opening out into the space 27h, are opened so that this space also is filled with pressure medium and extrusion takes place.

I claim:

1. Press for hydrostatic extrusion of tubes comprising a press stand, a pressure chamber comprising a highpressure cylinder displaceably arranged in the press stand, a die support, a die held by such holder sealing one opening of the cylinder, said die having an opening for forming a profile, and a punch insertable in the other opening of the cylinder for generating a pressure within a pressure medium enclosed in the pressure chamber and surrounding a billet for extrusion of the billet, a mandrel in the pressure chamber, a billet holder shaped like a piston dividing the pressure chamber into two spaces and having an opening for the mandrel, said piston holding the billet and the die pressed against the die support while the pressure chamber is closed, the billet holder having means thereon sealingly engageable against a billet in the pressure chamber, thereby separating a first space between the billet and the cylinder wall from a second space between the billet and the mandrel, a first and a second flow path through the billet holder opening out into the first and the second spaces, respectively, and valve means in the flow paths which open the flow paths at different pressure differences between the spaces on both sides of the billet holder.

2. Press according to claim I, in which the mandrel is axially displaceable.

3. Press according to claim I, in which the separating means comprises an annular rib on the end surface of the billet holder facing a billet and sealingly engageable against the end surface of the billet. 

1. Press for hydrostatic extrusion of tubes comprising a press stand, a pressure chamber comprising a high-pressure cylinder displaceably arranged in the press stand, a die support, a die held by such holder sealing one opening of the cylinder, said die having an opening for forming a profile, and a punch insertable in the other opening of the cylinder for generating a pressure within a pressure medium enclosed in the pressure chamber and surrounding a billet for extrusion of the billet, a mandrel in the pressure chamber, a billet holder shaped like a piston dividing the pressure chamber into two spaces and having an opening for the mandrel, said piston holding the billet and the die pressed against the die support while the pressure chamber is closed, the billet holder having means thereon sealingly engageable against a billet in the pressure chamber, thereby separating a first space between the billet and the cylinder wall from a second space between the billet and the mandrel, a first and a second flow path through the billet holder opening out into the first and the second spaces, respectively, and valve means in the flow paths which open the flow paths at different pressure differences between the spaces on both sides of the billet holder.
 2. Press according to claim 1, in which the mandrel is axially displaceable.
 3. Press according to claim 1, in which the separating means comprises an annular rib on the end surface of the billet holder facing a billet and sealingly engageable against the end surface of the billet. 